2nd part ECG basics PR interval and heart block

WPW syndrome LGL syndrome Heart Block 3 degrees and illustrations by Dr Salah Mabrouk Khallaf

1. ECG BASICSECG BASICS
22
ndnd
Lecture Lecture
PR interval and Heart BlockPR interval and Heart Block
By
Salah Mabruok Khalaf
South Egypt Cancer Institute
2017
Course of Medical Oncology
Medical Oncology department

2. PR interval

3. PR interval
•Definition: from the beginning of
the P-wave to the beginning of the
QRS complex .
•PR = Atr Depolar + AVN Delay
= P wave + isoelectric line
= 2.5 + (0.5-2.5) = 3-5 ss

4. Abnormal PR interval
•It is an interval
•So its abnormalities either
1- Shortened OR
2- Prolonged
According impulse passage through
natural block (AVN)
AVN
Atrium Ventricle

5. Short PR: < 3 ss
1-Preexcitation syndromes:
–WPW (Wolff-Parkinson-White) Syndrome.
–LGL (Lown-Ganong-Levine)
2-AV Junctional Rhythms.
3-Ectopic atrial rhythms originating near the
AV node.
4-Normal variant

6. WPW Syndrome
•An accessory pathway (called the "Kent" bundle) connects the right
atrium to the right ventricle (see diagram below) or the left atrium to the
left ventricle, and this permits early activation of the ventricles causing:
•1-short PR interval.
•2- delta wave
•3- Tall R wave
•4- Wide QRS

7. •Localising the accessory pathway
•An accessory pathway, bundle of Kent, exists
between atria and ventricles and causes early
depolarisation of the ventricle. The location of
the pathway may be deduced as follows:-
•LOCATION V1 V2 QRS axis
left posteroseptal (type A) +ve +ve left
right lateral (type B) -ve -ve left
left lateral (type C) +ve +ve inferior (90)
right posteroseptal -ve -ve left
anteroseptal -ve -ve normal

8. LGL (Lown-Ganong-Levine(
•An AV nodal bypass track into the His bundle exists, and this permits
early activation of the ventricles without a delta-wave because the
ventricular activation sequence is normal.
Atrium VentricleAVN

9. Lown Ganong Levine Syndrome
short PR interval, less than 3 small squares (120 ms(
no delta wave

10. AV Junctional Rhythms with retrograde atrial
activation (inverted P waves in II, III, aVF):
Retrograde P waves may occur before the
QRS complex (usually with a short PR
interval):

11. Ectopic atrial rhythms originating near the AV
node (the PR interval is short because atrial
activation originates close to the AV node;
the P wave morphology is different from the
sinus P)

12. II- Prolonged PR
•>0.20s > 5 ss
•In Heart block = AVN block:
•First degree AV block
•Second degree AV block
–Type I (Wenckebach)
–Type II (Mobitz)
•Third degree AV block = complete heart
block

13. First Degree AV Block
•PR interval is constant = same delay in each
one but there is still one P-wave per QRS.

14. First Degree AV Block

15. Second degree AV Block:
•Mobitz I Block (Wenckebach phenomenon): Here
there is progressive PR interval prolongation until a
P wave fails to conduct.
NO QRS
P P PPP

16. Mobitz I Block

17. Mobitz II Block:
sudden absent QRS complex
P
PPPP

18. Mobitz II Block
•2:1 or 3:1 Block: Occurs when every second
or third P wave conducts to the ventricles. P-
R interval remains normal in the conducted
beats.

19. Mobitz II Block

20. Third degree (complete) AV Block:
There will be no relationship between P-wave (atrial) rate and
QRS complex (ventricular) rate (AV Dissociation).
QRS complexes tend to be abnormally shaped due to
abnormal spreading of depolarization across the ventricles.

21. 40 bpm• Rate?
• Regularity? regular
no relation to QRS
wide (> 0.12 s)
• P waves?
• PR interval? none
• QRS duration?
Interpretation?3rd Degree AV Block